The disclosed invention relates to multicell photovoltaic semiconductor devices on a common substrate. The use of multiple monolithic cells on a common substrate where large photocurrents are generated is more desirable than the same area fabricated as a single cell or multiple interconnected single cell devices. The use of monolithic multi-cell construction reduces the output current and increases the output voltage linearly by the number of cells connected in a series string. Because of internal resistance losses are reduced in proportion to the square of the current, the overall internal power losses in multi-cell devices at high levels of illumination are greatly reduced.
In the fabrication of multi-cell devices on a common substrate, individual cells must be electrically isolated from one another. In the prior art, electrical isolation is created by the use of physical dielectric barriers between the cells, which increases fabrication cost and complexity. The invention described herein provides multiple diode strings that can be formed on a common substrate without the use of physical isolation. The disclosed invention does not require the use of a physical isolation barrier to achieve electrical isolation between cells in a multi-cell monolithic device. The invention is applicable to devices containing semiconductor materials where diodes can be fabricated with discrete P and N junctions.
In the prior art, multi-cell devices make use of physical trenches to achieve electrical isolation between cells. Most practical trench fabrication processes require the incorporation of multiple epitaxial layers into a multi-cell device. The requirement for multiple epitaxial layers further increases processing costs beyond the trench fabrication cost, and its implementation generally requires the participation of highly skilled technologists, as the multiple epitaxial layers have complex fabrication requirements.